The present specification relates generally to the field of integrated circuits and to methods of manufacturing integrated circuits. More particularly, the present specification relates to the use developer as a solvent to spread photoresist faster and then reduce the photoresist consumption.
Generally, conventional integrated circuit manufacturing processes involve the transfer of geometric shapes on a mask to the surface of a semiconductor wafer or layer above the semiconductor wafer. The semiconductor wafer corresponding to the geometric shapes, or corresponding to the areas between the geometric shapes, is etched away. The transfer of the shapes from the mask to the semiconductor wafer typically involves a lithographic process. Conventional lithographic processes include applying a pre-polymer solution to the semiconductor wafer, the pre-polymer being selected to form a radiation-sensitive polymer which reacts when exposed to ultraviolet light, electron beams, x-rays, or ion beams. The solvent in the pre-polymer solution is removed by evaporation, and the resulting polymer film is then baked. The film is exposed to radiation, such as, ultraviolet light, through a photomask supporting the desired geometric patterns.
The images in the photosensitive material are then developed by soaking the wafer in a developing solution. The exposed or unexposed areas are removed in the developing process, depending on the nature of the radiation-sensitive material. Then, the wafer is placed in an etching environment which etches away the areas not protected by the radiation-sensitive material. Due to their resistance to the etching process, the radiation sensitive-materials are also known as photoresists.
The high cost of photoresist pre-polymer solutions makes it desirable to devise methods of improving the efficiency of the coating process to minimize the amount of the polymer solution required to coat a substrate. Furthermore, thickness uniformity of the photoresist layer is an important criterion in the manufacture of integrated circuits. When the radiation is focused through the mask onto the coating, variations in thickness of the coating prevent the precise focus of the radiation over the entire surface of the wafer. Such precision is necessary to ensure satisfactory reproduction of the geometric patterns on the semiconductor wafer. Moreover, high precision is particularly important for advanced circuits with line width dimensions approaching 0.25 micron line widths and smaller.
Photoresist is often deposited to a substrate, or more particularly a wafer, by means of forming a puddle followed by spinning (i.e., spin coating). A large puddle of photoresist covering more than half of the substrate area is applied via a dispenser that directs a steady flow of resist in liquid form. The thickness of the puddle is of the order of a millimeter. The substrate is then spun at a speed ranging from 1,000 to 10,000 RPM to thoroughly spread out and remove the excess resist. This spinning results in a film thickness on the order on between a fraction of micrometer and a few micrometers. Therefore, only a small percentage of the photoresist material actually remains on the substrate. Most of the photoresist material dispensed is wasted, resulting in high cost and waste disposal problems.
During conventional photoresist spin coating, as much as 90% of photoresist material is spun away and wasted. Thus, there is a need to dispense photoresist material in a more efficient manner. Further, there is a need to dispense photoresist material that limits waste and increases uniformity of the dispensed photoresist material.
Thus, there is a need to reduce the expensive photoresist consumption by helping the photoresist material spread faster. Further, there is a need to use developer as a solvent to serve as an aid to reduce inefficient loss of photoresist material during photoresist spin coating. Further still, there is a need to reduce photoresist consumption in the spin coating process.
An exemplary embodiment of the invention is related to a method of using developer as a solvent to spread photoresist faster and reduce photoresist consumption. This method can include dispensing a developer solution onto an integrated circuit wafer, spinning the integrated circuit wafer to distribute the developer solution over the integrated circuit wafer, and dispensing a photoresist solution onto the integrated circuit covered with the developer solution.
Another exemplary embodiment is related to a resist dispensing system used in the dispensing of photoresist material on an integrated circuit wafer in an integrated circuit fabrication process. This system can include a wafer supporting structure configured to spin an integrated circuit wafer, a nozzle for dispensing a developer solution on the integrated circuit wafer, and a nozzle for dispensing a photoresist material on the integrated circuit wafer.
Another embodiment is related to a method for efficient dispensing of photoresist material onto an integrated circuit substrate. This method can include providing a developer coating onto an integrated circuit substrate, dispensing a photoresist solution onto the integrated circuit substrate having the developer coating, and rotating the integrated circuit substrate to distribute the photoresist solution over the integrated circuit substrate.